This invention relates in general to scroll saws and more particularly to improvements in the mounting of scroll saw blades.
Power scroll saws have enjoyed considerable recent popularity, due in large part to their ability to make the extremely accurate cuts required for finely detailed fret work and other intricate patterns. Modern scroll saws are either parallel arm saws or one piece C arm saws. The parallel arm saw includes separate upper and lower arms which pivot in tandem about vertically aligned pivot pins. The C arm saw is similar except that the two arms are part of a single C shaped arm structure which pivots about a pivot point located on the bight portion of the C arm.
The ability of scroll saws to achieve intricate cutting is due primarily to the extremely thin blades that are used and the resulting ability of the blades to cut sharp turns. However, the thin blades are susceptible to breaking, and it is essential for the blade to be kept under the proper uniform tension in order to prevent excessive blade tension or undue blade flexing, either of which can result in poor cutting action and early blade failure. In parallel arm saws, the blade tension is normally adjusted by tightening a tensioning rod which extends between the back ends of the two arms. An adjustment lever or knob on the front end of the upper arm is used for adjusting the blade tension in C arm saws. In both cases, the blade must be able to pivot relative to the arm, and the chucks or blade holders are thus pivotally mounted on the arms.
During operation of a scroll saw, the need to perform piercing or interior cuts is often encountered. This requires that the blade be removed and threaded through an opening in the wood before being attached again to the saw arms. The reverse procedure is required after each inside cut has been completed. Because of the need to frequently remove and reattach the saw blade, it is highly desirable for the blade to be mounted in a manner permitting it to be quickly and easily attached and detached. It is also important for the blade tension to be maintained constant before and after each blade change. The blade clamps that are ordinarily used are either tapered or round blocks that rock in grooved seats on the arms or clamp blocks that are pivotally pinned to the saw arms.
One type of blade holding system that has proven to be particularly effective in a parallel arm scroll saw includes a round or tapered blade clamp that seats in a groove in the lower arm in combination with a pair of upper clamp blocks which are pinned to the end of the upper arm. Blade removal is carried out by releasing the tension adjustment mechanism at the back ends of the arms, loosening the screw which clamps the blade between the upper clamp blocks, releasing the top end of the blade and threading it through an inside cut, and clamping the blade in the upper chuck again by retightening the screw.
The clamp elements in the upper chuck are a pair of flat metal blocks, one of which is pivotally pinned to the end of the upper arm. The blocks may be tightened to clamp the blade between them by tightening a machine screw. A roll pin extends through aligned apertures in the blocks to keep them from turning relative to one another about the screw axis.
Although this system functions well for the most part, it is necessary but not always easy to make certain that the top end of the blade is exactly centered in the upper blade clamp. If the blade is off center when clamped between the clamp blocks, the saw will not cut properly and the blade is subjected to excessive forces which can break it. Similarly, when a broken or damaged blade is replaced by a new blade, the blade must be centered in the lower chuck in order for the saw to operate properly.
The present invention is directed to an improved blade clamp for the top end of a scroll saw blade and also to a uniquely constructed tool which automatically centers the blade in the lower blade clamp.
The upper blade clamp is provided with a guide pin which is strategically located in order to properly and repeatably center the blade in the upper blade clamp. By virtue of its strategic location, the pin serves the dual purposes of connecting the two clamp blocks and also guiding the blade into the proper position so that it is precisely centered in the blade clamp when the lock screw is tightened.
The tool which is used to properly align the blade in the lower blade clamp takes the form of a flat bar provided with a recess and an intersecting groove. The recess has a configuration to closely receive the lower blade clamp. The groove in the tool intersects with the recess at a location to assure that when a blade is inserted into the groove and butted at its end against the lock screw of the blade clamp, the blade will be properly aligned and centered in the clamp.
By providing for the proper location and alignment of the blade in both blade clamps, the present invention facilitates blade changes and at the same time assures proper cutting action because the blade is maintained at the proper position and under proper tension at all times. The overall result is that the saw can be operated easily and accurately even by inexperienced operators, while the time and difficulty involved in removing and replacing blades is reduced substantially in comparison to other scroll saws.